Applicant claims priority under 35 U.S.C. xc2xa7119 of German Application No. 100 41 696.9-12 filed Aug. 24, 2000.
1. Field of the Invention
The present invention relates to a toothed gear including an outer toothed rim, a hub and a profiled bridge area connecting the toothed rim and the hub as one piece, the bridge area being connected to the toothed rim and to the hub in different planes.
2. The Prior Art
Blanks for such toothed gears are known from DE-PS 908 317. Such blanks are one-piece gear wheels that can be manufactured by pressing or forging methods. The outer toothed rim and the hub of such gear wheels are connected to each other by a completely closed, disk-like bridge area. The disk-shaped bridge area preferably consists of alternately arched, circular sectors which, on account of their shape, are tied to the toothed rim and to the hub in different planes. The disk-like bridge area is required in connection with such toothed gears in order to satisfy strength requirements and to avoid vibration phenomena that may lead to the development of noise. Such a disk-shaped bridge area requires relatively high material expenditure.
Toothed wheels with bridge areas in the form of spokes are known from U.S. Pat. No. 3,371,549, where the spoke-like elements are always tied in the center both to the inner side of the toothed rim and to the hub. Such spoke-like bridge areas may be profiled as well. The blanks for toothed gears of this type manufactured by forging or pressing methods are hardened by thermal treatments. Such heat treatments cause substantial phenomena of distortion between the toothed rim and the hub that have to be attributed to the special shapes of the bridge areas.
The problem of the invention is to optimize the area of the bridge area of a toothed wheel that is to be producible by pressing or forging methods with respect to its distortion behavior in heat hardening processes and in regard to required weight reductions.
The problem is solved in accordance with the invention with a toothed gear including an outer toothed rib, a hub and a profiled bridge area connecting the toothed rim and the hub as one piece. The bridge area is connected to the toothed rim and to the hub in different planes. Moreover, the bridge area is formed by uniformly spaced, bridge spokes uniformly distributed over the circumference. The bridges are arranged in an alternating manner on both sides of a center plane. Owing to the arrangement of the spoke-like bridges, distortion phenomena are avoided to a large extent in heat treating the blanks for the toothed gears. Shaping the bridge area in the form of individual spokes leads to substantial material savings combined with adequate strength values.
In a preferred embodiment, each spoke is a section of an imaginary disk connecting the toothed rim and the hub, the disk being profiled in the peripheral direction as a periodic circular function. Such toothed gears can be shaped with Particularly good results, and they exhibit good strength properties and vibration damping properties particularly if each bridge is formed in the area of maximum amplitude of the circular function.
It was found that it is favorable to arrange the bridges in an alternating manner in two planes extending parallel with the center plane and to space the bridges from the center plane.
The strength properties are increased by an embodiment of the toothed gears where the bridges have widened transition areas directly connecting the bridges to both the hub and to the inner side of the tooth rim.